This invention relates to a data recording system, and more particularly to a recording system having flexibility to respond to the electrical state of devices connected to any one of a plurality of terminals either singularly or in groups of various combinations.
With the increase in size and complexity of modern large industrial establishments it is becoming evermore essential to provide administrative, engineering, maintenance and statistical information regarding the electrical state of various devices functioning in the system. Typically, the electrical devices may be detectors responsive to the opened and closed position of valves in a complex piping system of a chemical processing plant. Such electrical devices may also respond to the amount of telephone service used by a customer or group of customers, that is, the precise time of each telephone usage, whether the call was incoming or outgoing, as well as various other statistical information regarding telephone service. In yet another example showing the complete flexibility of the present invention is the monitoring of electrical devices associated with parking spaces in a group of parking lots to monitor when such space is filled, how long each space was filled and the time when each space is vacated. Changes in the electrical state of the devices in each of the above examples may be translated into a recording of events, measurement of real or elapsed time, preprocessing and formating the data and then providing a tape or a hard copy of the results.
For purposes of explanation, consider the use of the invention in the telecommunications industry where it has been quite common to provide at a telephone central office traffic monitoring equipment. This equipment usually consists of traffic registers and counters (peg count meters, etc.) providing facilities for obtaining information about all call busy attempts, group busy, partial digits, traffic usage, position disconnect and answering time registration as well as other miscellaneous data on the various circuits in the office. This equipment is usually mounted in relay racks because of its bulk and size and provides individual line indications relative to an associated circuit. Usually no recordings of the figures on the various meters and counters are included, however, occasionally facilities for photographing the information are provided. More contemporary telecommunications systems are equipped with devices known as traffic usage recorders to provide traffic data by means of a switch count. Circuit terminals are scanned at predetermined intervals and those found busy are recorded on registers for the various circuit groups with busy conditions accumulated at the end of an hour or other predetermined period to indicate traffic load that was carried.
Telephone customers are served by a variety of types of central offices, that is, step-by-step, cross bar, electronic, etc., and it is impractical to provide a dedicated path for every originating equipment line, through the switching machine, to every possible termination (or telephone number) served by a particular central office. Realizing the impracticality of a dedicated path for every originating line, most central offices are designed to bring customers into the office in line groups, whereby a group of approximately 200 customers are served by 20 or less originating switches operating on "paths" or "links" to switch calls to the office. The number of customers that can be served by this form of concentration is a function of the number of calls placed by the 200 customers and the "holding time", or length of a call. In the telephone industry, "calling rate and holding time per call" is translated into "hundred call seconds (CCS) usage" or the usage stated in hundreds of call seconds. Since calling habits vary widely between customers, and the times of their calling varies by the hours in each day, it is very desirable to effect a "balance" within each group and between line groups to obtain an even flow of calls throughout the office throughout the day. The utopian situation would be to have the same number of calls handled by each line group for every 24 hour period. This would permit serving the maximum number of customers with the minimum capital expenditure for switching equipment.
In actual practice, telephone service customers are assigned to line groups by types of services that is, coin telephone, individual lines, two party lines, four party lines, business, and other types of telephone service. Traffic engineers in the telephone industry have established tables based on theories that are used to state the maximum number of CCS usage that can be assigned to a group of lines. These theories assume a CCS usage value for each of the types of telephone service provided. Lines are then assigned so that a line group is filled up to the CCS usage capacity for a particular central office. Theoretically, these maximums are based on the busy hour of the busy day of a busy season. This theoretical approach to offic loading and balancing works well when labor and equipment are relatively inexpensive, office loads are not exceptionally heavy and the calling rates are low. With new communications services now being offered such as WATS, data transmission, computer access lines, teletype services, in addition to others, the old "average" calling rate and holding times are fast becoming obsolete. The telephone industry spends many man hours, dollars and material attempting to "balance" calling loads through the various switching machines.